FAS2520 900 GB SAS Internal Drives only 3 Gbps Interface speed?

When checking the interface speed for FAS2520 internal drives, the HWU states that the 900 GB (X488A-R5) SAS Drives only seems to have an interface speed of 3 Gbps. For all other SAS drives the HWU states an interface speed of 6 Gbps.

Is this a typo?

If not, is the interface speed of the internal bay throttled down to only 3 Gb/s if using those 900 GB SAS Drives and does this even affect addtionally attached 6 Gb/s SAS Shelves like the DS2246?